<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
    <link rel="stylesheet" href="../css/demo-transition.css">
</head>
<body>
    <div class="box demo-1">

    </div>
    <div class="box demo-2">
        <div class="cell"></div>
    </div>
    <div class="box demo-3">
        
    </div>
</body>
<script>
    let runend = () =>{console.log('runend')}
    let $loading = document.querySelector('.demo-1')
    $loading.addEventListener('transitionend',runend)
</script>
</html>